Silver-indium contact



Patented May 9, 1939 UNETE s'rArss' PATENT OFFICE SHNER-INDIIM CONTACTNo wing.

Application August 6, 1938,

Serial No. 223,507

This invention relates to electric contacts.

An object of the invention is to improve the characteristics of electriccontact elements containing silver.

5 Another object of the invention is to provide a silver base contactmaterial which is highly resistant to tarnishing and therefore will notform a layer of high contact resistance.

A still further object is to provide a new con- 1 tact material whichcan be used under severe electrical conditions, without welding.

It is a further object of the invention to provide a contact capable ofoperating on high frequency at heavy current values, without objec- 15tionable contact metal transfer.

Other objects of the invention will be apparent from the followingdescription taken in connection with the appended claims.

The present invention relates to an electric contact and the combinationof elements therefor, methods of manufacture and the product thereof,brought out and exemplified in the disclosure hereinafter set forth, thescope of the invention being indicated in the appended claims.

35 While a preferred embodiment of the invention is described herein, itis contemplated that considerable variation may be made in the method ofprocedure, and the combination of elements, without departing from thespirit of the m invention.

The present invention comprises an improvement in silver electriccontact elements, and especially in contact elements formed of at least70% of silver. According to the invention, the

;;.-, contacts are improved by the addition of indium.

The contacts may be composed of silver and indium, accordingly. Theingredients may bepresent in approximately the following proportions:

Indium 0.1 to 21% Silver Balance It is likewise possible to improve thecharacteristics of silver alloys containing additional in- 5 gradients,by the addition of indium; thus silver alloys containing beryllium,magnesium, zinc.

cadmium, copper, gold, nickel, manganese, palladium group elements,platinum group elements,

silicon, titanium and zirconium can be improved 50 by the addition ofindium in substantially the proportions indicated above.

We have found that silver and indium, up to 21% indium, alloy veryreadily and the cast ingots have an extremely clean surface. The alloys55 can be readily swaged and drawn to wires from which contacts may beprepared by a screw machine operation or by cold heading. Silver-indiumalloys may also be rolled in the form of sheet, and contacts may bepunched from sheets. Silver-indium alloys lend themselves very readilyto be prepared in the form of contact bimetals, in which one sideconsists of a base metal, such as an alloy of iron, nickel or a copperbase material, and silver-indium material on the other side. The natureof the alloy is such as 1 to lend itself readily to the formation ofelectrical contacts by beading or fusing the alloy directly to thesurface of a base metal blank, such as a rivet, screw or disc, etc. Theease with which these materials can be rolled has reduced greatly scraplosses and produced smooth surfaces which are ideally suitable for themanufacture of electric contacts.

In a number of contact applications, silver is mixed with refractorymaterials, taken from the group of tungsten and molybdenum, or theircompounds. These materials are prepared either by mixing the powderstogether, pressing same and hot and cold working same into suitableforms from which contacts can be prepared. We 5 have found that theaddition of indium to the silver base used in such contact combination,is extremely beneficial for several reasons. Indium improves thefluidity of molten silver, and when such contact materials are producedby an impregnating process the presence of indium in percentages up to21%, will improve the "alloying or impregnating action of the liquidsilver base. Therefore, a structure is obtained which is much moreuniform and homogeneous, and 5 at the same time it is possible toproduce pieces of much larger cross section by substituting asilver-indium alloy for fine slver. Indium has the definite advantage,furthermore, of having a very low melting point of 155 degrees C., but avery high boiling point of 1450 degrees C. It, therefore, mixtures arebeing prepared by using powders of the elements incorporated into thefinal mixture, sintering temperatures can be used which arecomparatively high, without fearing the loss of any indium, due tovaporization.

It is possible also to produce a much stronger mixture that way, becausethe materials can be prepared by having a liquid phase present, whichwill cement not only the silver particles, but also the refractoryparticles, much better.

We have limited ourselves in the indium content to 21%, because we havefound that the most desirable contacts can be prepared from an alphasolid solution of indium in silver. The solid solubility of indium insilver at room temperatures, is approximately 20.4%, while at 693degrees 0., it is 21%.

When operated on voltage regulators, such as used in regulation ofautomotive generators, the material of the present invention, operatingagainst a high silver alloy of a different composition, such asa-silver-palladium alloy, maintained perfect regulation. This operationat frequencies between 50 and 400 cycles, for periods of in excess of500 hours, gave contact resistance values of extremely low order, 0.4 to0.5 mllliohms. After continuous operation exceeding 750 hours, ourresistance value is in the order of M of that normally encountered onalloys previously adopted for this type of service.

On applications for standard relay equipment, operating on a directcurrent, it has been found that the use of alloys of the type covered bythe present combination, will increase the critical current value orvalue of failure current, between 80 and 100% over other commercialalloys at present available. The material does-not transfer as readily,which reduces the tendency to failure by sticking, because by relativelyhigh increases in current density, due to reduction in area.

tact. At the same time, definite "seating" of the contacts is effectedwith extremely small dimensional displacements, so that it is possibleto accurately maintain the shape'and placing of the contacts where suchfactors materially aflect the operation of the equipment on which thecontacts are a part.

While the present invention, as to its objects and advantages has beendescribed herein, as carried out in specific embodiments thereof, it isnot desired to be limited thereby, but it is intended to cover theinvention broadly, within the spirit and scope of the appended claims.

What is claimed is:

1. An electric contact member containing as an essential ingredient,silver to which has been added indium, in quantities ranging from 0.1 to21%.

2. An electric contact, consisting of an alloy of 0.1 to 21% indium,balance substantially all silver.

3. An electric contact member composed of a refractory metal base and asilver alloy containing 0.1 to 21% indium.

4. An electric contact member formed oi a bonded mass of refractorymetal powders selected from the group consisting of tungsten andmolybdenum together with a silver alloy containing 0.1 to 21% indium.

FRANZ R. HENSEL. KENNETH L, EMMERT.

